In the formation of integrated circuits, devices such as transistors are first formed at the surface of a semiconductor substrate, which is a part of a wafer. Interconnect structures are then formed over the semiconductor substrate and the devices. Electrical connectors such as metal bumps are formed on the surface of the semiconductor wafer, so that the devices can be accessed. The wafer is sawed into a plurality of semiconductor dies.
The packaging of the semiconductor dies may be performed through reflow processes. In the packaging, solder regions are reflowed to bond the semiconductor dies to other package components such as device dies, interposers, package substrates, or the like. After the bonding, a gap may exist between a semiconductor die and the respective bonding package component. An underfill is typically dispensed into the gap and cured. The underfill protects the solder regions and the surrounding structures.